FULL PAPER
DOI: 10.1002/adfm.200700797
One-Step Ionic-Liquid-Assisted Electrochemical Synthesis of
Ionic-Liquid-Functionalized Graphene Sheets
Directly from Graphite**
By Na Liu, Fang Luo,* Haoxi Wu, Yinghui Liu, Chao Zhang, and Ji Chen
Graphite, inexpensive and available in large quantities, unfortunately does not readily exfoliate to yield individual graphene
sheets. Here a mild, one-step electrochemical approach for the preparation of ionic-liquid-functionalized graphite sheets with the
assistance of an ionic liquid and water is presented. These ionic-liquid-treated graphite sheets can be exfoliated into
functionalized graphene nanosheets that can not only be individuated and homogeneously distributed into polar aprotic
solvents, but also need not be further deoxidized. Different types of ionic liquids and different ratios of the ionic liquid to water
can influence the properties of the graphene nanosheets. Graphene nanosheet/polystyrene composites synthesized by a
liquid-phase blend route exhibit a percolation threshold of 0.1 vol % for room temperature electrical conductivity, and, at
only 4.19 vol %, this composite has a conductivity of 13.84 S m1, which is 3–15 times that of polystyrene composites filled with
single-walled carbon nanotubes.
1. Introduction
Recently, graphene (graphite sheets that are one-atom-thick
layers of sp2-bonded carbon) has attracted a tremendous
amount of attention.[1] It is predicted to have remarkable
properties, such as large thermal conductivity comparable to
the in-plane value of graphite, superior mechanical properties,
and excellent electronic transport properties.[2] The exfoliation
of expanded graphite results in separation of the graphite
sheets into graphene nanosheets (GNSs).[3] The high aspect
ratio and the large surface area of GNSs are responsible for the
much lower percolation threshold and better electrical
conductivity of conducting polymer composites than composites with micrometer-scale conventional reinforcements.[4]
Conducting polymer composites have many potential
applications in electromagnetic interference shielding for
electronic devices and electrostatic dissipation, where high
electrical conductivity of the composite material is the most
[*] Dr. F. Luo, N. Liu, H. X. Wu
College of Chemistry
Northeast Normal University
Changchun 130024 (P.R. China)
E-mail: [email protected]
Dr. Y. H. Liu, Dr. C. Zhang, Prof. J. Chen
Changchun Institute of Applied Chemistry
Chinese Academy of Sciences
Changchun 130022 (P.R. China)
[**] This project was sponsored by the Scientific Research Foundation for
Returned Overseas Chinese Scholars, the State Education Ministry,
and the Scientific Innovation Foundation for Undergraduates, Northeast Normal University. Supporting Information is available online
from Wiley InterScience or from the author.
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critical requirement.[5] Recently, much attention has been
given to the use of single-walled carbon nanotubes (SWNTs) in
composite materials to utilize their exceptional mechanical and
electronic properties.[6] SWNTs have a cylindrical nanostructure with a high aspect ratio, and a large p-electronic surface
forms by the rolling-up of a two-dimensional (2D) graphene
sheet. It is well-known that pristine SWNTs are generally
insoluble in common solvents and polymers, and that it is
difficult to chemically functionalize them without altering the
nanotubes’ desirable intrinsic properties. Adsorption of
organic molecules on SWNTs by means of van der Waals
and p–p stacking interactions has been investigated to modify
their chemical and physical properties and to improve their
processability.[7] However, many problems still need to be
solved before SWNTs can be successfully incorporated into
composite materials. The three biggest problems are the fact
that SWNTs easily clump together during processing, the
difficulty of controlling their diameter by the way the carbon
sheet is rolled, and the high cost of their production.[8]
As we know, a GNS is also a 2D system with very strong sp2
bonds, causing a threefold-coordinated planar structure with
the remaining pz orbital perpendicular to the plane, so that GNS
has a layer structure with high aspect ratio, a large p-electronic
surface, and requires no helicity control.[9] Furthermore, most
importantly, GNS is much cheaper than SWNTs. Therefore, it is
possible to obtain functional composite materials with highperformance chemical and physical properties by modification
of GNS with organic molecules. As Nicholas A. Kotov wrote in
his review in Nature[10] ‘‘When carbon fibers just won’t do,
but nanotubes are too expensive, where can cost-conscious
materials scientists go to find a practical conductive composite?
The answer could lie with graphene sheets.’’
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Adv. Funct. Mater. 2008, 18, 1518–1525
Currently, it is deemed that exfoliation of graphite oxide is
the only way to produce stable suspensions of quasi-2D carbon
nanosheets.[11] Graphite oxide is prepared by treating graphite
with strong aqueous oxidizing agents such as fuming nitric acid/
potassium chlorate or sulfuric acid/potassium permanganate.[12]
In contrast to pristine graphite, these graphite-derived sheets
are heavily oxygenated, bearing hydroxyl and epoxide functional groups, which make them strongly hydrophilic, readily
dispersed in water, and incompatible with most organic
polymers.[13] In addition, graphite oxide, unlike graphite, is
an electrical insulator, which limits its usefulness for the synthesis
of conductive nanocomposites. In order to solve the above
problems, Stankovich et al.[11] treated graphite oxide with
phenyl isocyanate for 24 h, which added hydrophobic chemical
groups to the surface. Subsequently, a small amount of the
reducing agent dimethylhydrazine (at 80 8C for 24 h) was
further used to reduce graphite oxide in order to restore the
conductivity of the resulting composite material. Although the
authors obtained a composite with excellent structural and
conductive characteristics, the surface modification to produce
GNS brought inconvenience and pollution.[14]
Interest in ionic liquids (ILs) has increased dramatically in
the past decade as their unique properties have been exploited.
Because of their specific properties, such as negligible vapor
pressure, low toxicity, high chemical and thermal stabilities,
and a wide range of organic and inorganic compounds, ILs
have been proposed as ‘‘green’’ alternatives to conventional
organic solvents in a range of applications, such as synthesis,
catalysis, and liquid–liquid extractions.[15] Particularly in
electrochemistry, they show a relatively wide potential window
and high conductivity and allow studies to be undertaken
without addition supporting electrolyte. Recently, Fukushima
et al.[16] reported that an IL gel with carbon nanotubes opened
a new possibility of ILs as modifiers for carbon nanotubes.
Upon being ground into ILs, carbon nanotubes are untangled,
and the resultant fine bundles form a network structure. This is
due to the possible specific interaction between the imidazolium ion component and the p-electronic nanotube surface.
The resultant gelatinous materials, consisting of highly
electrically conductive nanowires and fluid electrolytes, can
be utilized for a wide variety of electrochemical applications.
ILs allow for noncovalent and covalent modifications of carbon
nanotubes and fabrication of polymer composites with
enhanced physical properties.[16] It provides us with new
Scheme 1. Experimental set-up diagram (left) and the exfoliation of the
graphite anode (right).
Adv. Funct. Mater. 2008, 18, 1518–1525
opportunities for the electrochemical functionalization of
graphite, such that an extremely rapid and mild green chemical
functionalization process results. Our experimental setup is
drawn schematically in Scheme 1. In the work reported here, this
concept was first utilized to fabricate a kind of IL-functionalized
GNS (abbreviated as GNSIL). In addition, the electrical
conductivity of the GNSIL/polystyrene composite was also
investigated.
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N. Liu et al. / Ionic-Liquid-Assisted Electrochemical Synthesis of Graphene
2. Results and Discussion
The GNSIL was prepared by the electrochemical functionalization of graphite. In a typical synthesis, 10 mL 1-octyl-3methyl-imidazolium hexafluorophosphate ([C8mim]þ[PF6])
and 10 mL water were used as the electrolyte. A static potential
of 15 V was applied between the two graphite rods. After
corrosion for 6 h at room temperature, a black precipitate of
GNSC8P was obtained at the bottom of the reactor. The
obtained GNSC8P was used for the following discussion. Figure 1
shows transmission electron microscopy (TEM), field-emission
scanning electron microscopy (FESEM), and atomic force
microscopy (AFM) images of GNSC8P. The TEM (Fig. 1a) and
FESEM (Fig. 1b) observations show that the average length of
GNSC8P was up to 700 nm with a width of 500 nm, and the
sheets were crumpled. The AFM sample was prepared by
ultrasonic treatment of GNSC8P in N,N-dimethylformamide
(DMF) at 1 mg mL1. The AFM image reveals exfoliated
GNSC8P with average thickness ca. 1.1 nm (Fig. 1c; see also
Supporting Information), leading to the conclusion that
complete exfoliation of graphite down to individual GNSC8P
was indeed achieved under these conditions. While a pristine
graphene sheet is atomically flat with a well-known van der
Waals thickness of ca. 0.34 nm, GNSC8P is expected to be
thicker owing to the presence of functionalized hydrocarbon
chains attached to the GNS slightly above and below the
original graphene plane.
In order to probe the interactions between the GNS and the
imidazolium of the ionic liquids described in this paper, we
employed X-ray photoelectron spectroscopy (XPS) and
Raman, Fourier transform infrared (FTIR), and X-ray powder
diffraction (XRD) analysis. When the GNSs were functionalized with ILs, the ILs could be connected to the surface of the
GNS, resulting in GNSIL. The connection of ILs to the surface
of the GNS was first characterized and verified by XPS
measurements, as presented in Figure 2a. The GNSC8P exhibits
a well-defined peak at 399.84 eV (Fig. 2a, curve 2), which was
not recorded for natural graphite (Fig. 2a, curve 1). Such a peak
is due to the presence of nitrogen atoms (N 1s) on the surface of
the GNS, and is indicative of the effective connection of
imidazolium ions to the GNS. Further careful analysis using
nonlinear regression indicated that the main peak at 399.84 eV
included modes at 399.80 and 401.51 eV, implying that two
different types of nitrogen atoms may be involved in the
imidazolium ion connected to the GNS surface. Because the
two nitrogen atoms in the free imidazolium ion may essentially
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Figure 1. a) TEM, b) FESEM, and c) tapping mode AFM height images of GNSC8P obtained in [C8mim]þ[PF6] and water (volume ratio 1:1) as electrolyte
and at 15 V applied potential.
have the same binding energy, the two peaks of nitrogen atoms
on the GNSC8P may consequently result from the interactions
between the imidazolium ion and the GNS. Additional
evidence of the formation of GNSC8P was provided by Raman
spectroscopy, which is one of the key analytical techniques
used in the characterization of GNS. Figure 2b shows typical
Raman spectra of natural graphite (curve 1) and GNSC8P
(curve 2). In the Raman spectrum of natural graphite (Fig. 2b,
curve 1), two peaks were observed, at 1593 cm1 and 1353 cm1.
The peak at 1593 cm1 corresponds to an E2g mode of graphite
and is related to the vibration of sp2-bonded carbon atoms in a
2D hexagonal lattice, such as in a graphite layer. The peak at
1353 cm1 is associated with vibrations of carbon atoms with
dangling bonds in plane terminations of disordered graphite.[17] In Figure 2b, curve 2, Raman modes are weak and
broad due to a high level of disorder of the graphene layers,
suggesting that defects in GNSC8P increased during the
functionalization process. The presence of IL groups was also
confirmed by FTIR analysis (Fig. 2c), in which the presence of
the C–H stretching bands located at 2923 cm1 and 2853 cm1,
and the C–H vibration at 1454 cm1, as well as the imidazolium
framework vibration at 1616 cm1, was evidenced. The XRD
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patterns of natural graphite (Fig. 2d, curve 1) and GNSC8P
(Fig. 2d, curve 2) exhibit the 002, 101, and 004 graphite
diffraction peaks, as labeled in Figure 2d, indicating that the
structure is preserved after the functionalization process.
However, the broad diffraction peaks of GNSC8P powder
hinted that the IL group can influence the crystallization of the
GNS in the functionalization process. The IL group content in
GNSC8P was determined quantitatively by thermogravimetry
(TG). Figure 2e shows the weight loss curve of the sample. The
first weight-loss region, from 100 to 210 8C, is related to
removal of physisorbed water. The second step, from 214 to
450 8C, has a weight loss of 6% that is caused by the decomposition of the surface-attached IL groups. Thus, it is suggested
that GNSC8P contains 6 wt % IL groups. All the above results
clearly indicate that the IL groups were connected to the
surface of the GNS.
Compared with the graphite oxide, our obtained GNSC8P no
longer disperses in water, but readily forms stable and homogeneous dispersions in polar aprotic solvents such as DMF,
dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP)
solution after a brief ultrasonic treatment. This potential
property makes GNSC8P an ideal candidate for an advanced
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Figure 2. a) N 1s region in XPS, b) Raman (solid scan, excitation wavelength 514.5 nm), c) FTIR, and d) XRD (Cu Ka) spectra of natural graphite (1) and GNSC8P
(2). e) TG (heating rate 10 8C min1, N2 flow 100 mL min1) curve of GNSC8P.
filler material and for facilitating synthesis of functional graphite/
polymer composites. The stable dispersions of polystyrenecoated GNSC8P were also analyzed by UV-vis spectroscopy; the
results were shown in Figure 3. The UV-vis spectrum of the
GNSC8P/polystyrene composite dispersed in DMF possesses
similar features to that of polystyrene itself. In the spectra of
the colorless filtrate, obtained by filtration of the GNSC8P/
polystyrene composite dispersion through a polytetrafluoroethylene (PTFE) syringe membrane filter (0.45 mm pore size),
the intensity of the signal arising from the polystyrene is very
small, indicating that the polystyrene is strongly attached to the
GNSC8P surface.
Adv. Funct. Mater. 2008, 18, 1518–1525
On the basis of the investigation described above, the
mechanism for the formation of the GNSIL was speculated to
be the following. During the electrochemical reaction process,
the cation of the IL is reduced on the cathode, which means
that an electron is added to the IL molecule. According to
quantum chemical semiempirical calculations,[18] the unpaired
electron is located mainly on the C2 carbon of the
imidazolium ring contained in the IL (shown schematically
in Fig. 4a). The reduction of the cation, in principle, leads to
the formation of the 1-octyl-3-methylimidazolium free radical.
The radical can combine with one of the electrons of the
p-bond of the GNS, under formation of GNSIL. Thus, the
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Figure 3. UV-vis spectra of the polystyrene-coated GNSC8P composites
dispersed in DMF (concentration of GNSC8P/polystyrene composite in
DMF is 0.03 mg mL1), polystyrene dispersed in DMF (concentration of
polystyrene in DMF is 0.03 mg mL1), and the filtrate obtained by passing
the GNSC8P/polystyrene dispersion through a 0.45 mm PTFE membrane
filter.
Figure 4. Schematic illustrations of a) the formation of the 1-octyl-3methylimidazolium radical and b) how the GNSILs are attracted to similar
groups in the polymer.
GNSILs can be intimately mixed with many organic polymers
because the hydrophobic groups attached to the GNS are
hydrophobic ILs 1-octyl-3-methyl-imidazolium hexafluoroattracted to similar groups in the polymer, as shown
phosphate ([C8mim]þ[PF6]), 1-octyl-3-methyl-imidazolium
schematically in Figure 4b.
tetrafluoroborate ([C8mim]þ[BF4]), and 1-butyl-3-methylIt has been recognized that many ILs are hygroscopic and
imidazolium hexafluorophosphate ([C4mim]þ[PF6]) in water
can absorb a significant amount of water from the atmosphere.
with volume ratio 1:1 as electrolyte to synthesize the GNSILs
The physical properties of ILs, such as polarity, viscosity,
GNSC8P, GNSC8B, and GNSC4P, respectively. The experimental
solubility, and conductivity, not only change with the presence
of water but also depend on the
amount of water absorbed. In order
to investigate the influence of ILs and
the ratio of ILs to water on the character of the GNSILs, we conducted two
comparison experiments. In the first,
different volume ratios of the hydrophilic IL 1-octyl-3-methyl-imidazolium
chlorine ([C8mim]þCl) to water (1:0,
1:1, 1:3, 1:5, 1:8, 1:10, 1:15) were used
as an electrolyte to produce GNSILs
(GNS0, GNS1, GNS3, GNS5, GNS8,
GNS10, GNS15). Figure 5a shows the
dispersions of GNS0, GNS1, GNS3,
GNS5, GNS8, GNS10, and GNS15 in
DMF. The vial with GNS0 contained
visible precipitates, indicating poor
dispersion, whereas the black dispersions of the other GNSILs in DMF with
other volume ratios contained no
visible precipitates and were stable
and homogeneously distributed for
weeks. Under the same preparation
conditions, GNS5 has the highest yield. Figure 5. Photographs of a) GNS0, GNS1, GNS3, GNS5, GNS8, and GNS15, and b) GNSC8P, GNSC8B, and
In the second experiment, we used the GNSC4P dispersed in DMF after ultrasonication.
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results showed that the above three GNSILs can form a stable
and homogeneous phase in DMF for weeks (Fig. 5b).
Figure 6 shows UV-vis spectra of neat [C8mim]þCl, natural
graphite, GNS3, GNS5, GNS8, and GNS10. As the figure shows,
[C8mim]þCl and natural graphite have a maximum absorption at 268 and 231 nm, respectively, while GNS3, GNS5, and
GNS8 have two absorption peaks. With the increase of the ratio
of water to IL in the electrolyte, the absorption peaks (near
that of [C8mim]þCl) of GNS3, GNS5, and GNS8 have an
obvious blue-shift to 249, 248, and 244 nm, respectively.
Moreover, GNS10 has the same absorption as natural graphite.
Consequently, this absorption should be assigned to the
imidazolium ring. As a result, it is reasonable to suppose that
there is some kind of interaction between GNS and the
imidazolium ring of the IL, and water can effective influence
the content of the IL groups in the product.
The above results demonstrate that water is one of the key
factors for determining the character of the GNS. ILs are
complex molecules where coulombic forces, hydrogen bonds,
and van der Waals forces all participate in the interaction
between the molecules, with the hydrogen bonds being probably the most important forces in ILs.[19] It is well established
that water is accommodated in the IL structure by establishing
hydrogen bonds with both the anion and the cation, leading to a
decrease in value of the IL’s physical properties such as
viscosity by means of a reduction of the electrostatic attractions
between the ions, and therefore a decrease of the overall
cohesive energy. Low water content forces the IL to rearrange
into a new, different internal order in which more water can be
accommodated, until the point where further addition of water
leads to complete solvation of the ions and to the appearance of
water molecules not hydrogen-bonded to the IL, and thus to a
new structural rearrangement leading to an increase in value of
the physical properties mentioned before.[20] The only
explanation for their greater lipophilicity is the hydrogen
bonds that exist between the anions and cations, as discussed
above, which decrease the interactions between the ions, leading
to enhanced lipophilicity.
In order to investigate further the influence of ILs on the
character of the GNSILs, we prepared the electrically conductive composites GNSC8P/polystyrene, GNSC8B/polystyrene,
GNSC4P/polystyrene, and GNS5/polystyrene. Figure 7 shows
the volume electrical conductivity measured by a standard
four-probe method. The conductivity of pure polystyrene is
about 1014 S m1. At a GNSC8P content of about 0.1 vol %, a
sharp increase, which is known as the percolation transition,
emerges when the filler content reaches a critical value. Apart
from a very low percolation threshold, a rapid increase of
conductivity was observed between 0.1 and 0.38 vol %, where
the conductivity changed from 105 to 5.77 S m1. At loading levels in excess of 2.64 vol %, the conductivity, about
7.14 S m1, increased only moderately. The conductivity shows
a 30-fold increase from 0.47 S m1 at 0.13 vol % to 13.84 S m1
at 4.19 vol %. Moreover, the percolation transition of GNSC8B/
polystyrene and GNSC4P/polystyrene composites is about 0.13
and 0.37 vol %, respectively, and the highest conductivity is
about 6.59 and 3.61 S m1, respectively. Surprisingly, the
GNS5/polystyrene composite, where GNS5 was obtained in the
presence of the hydrophilic IL [C8mim]þCl and water, has
no conductivity. We speculated that the GNS was possibly
oxidized by Cl2 or O2 produced on the anode. In order to test
our speculation, the reducing agent sodium dithionite was
added to the electrolyte and then GNS5D was obtained under
the same preparation conditions. The conductivity of the GNS5D/
polystyrene composite was as high as that of the GNSC4P/
polystyrene composite. The results indicate that the anion does
indeed have a crucial effect on the conductivity of GNSILs. The
best conductivity (13.84 S m1) of our GNSC8P/polystyrene
composite is 3–15 times higher than the values reported for
SWNT-filled polystyrene composites.[21] Moreover, in contrast
Figure 6. UV-vis spectra of neat [C8mim]þCl, natural graphite, GNS3,
GNS5, GNS8, and GNS10 dispersed in DMF after ultrasonication.
Figure 7. Electrical conductivity of GNSC8P/polystyrene, GNSC8B/polystyrene, GNSC4P/polystyrene, and GNS5D/polystyrene composites.
Adv. Funct. Mater. 2008, 18, 1518–1525
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a topic of interest. Further work is in progress to evaluate the
possibility of synthesizing a family of composites with differing
properties and determining the mechanical properties of the
composites.
4. Experimental
Figure 8. The TG (heating rate 10 8C min1, N2 flow 100 mL min1) curves
of a) polystyrene and b) GNSC8P/polystyrene composite.
to those reports, our GNSIL/polystyrene composites are
prepared by standard industrial technologies such as molding
and pressing; such matters are crucial if nanotechnology is to be
applied in the real world.
The thermostability of the GNSC8P/polystyrene composite
will now be discussed and compared with that of bulk
polystyrene. Figure 8, curve a, shows that the main step of
bulk polystyrene degradation is from 300 to 450 8C, which is
attributed to main-chain pyrolysis,[22] commencing at about
340 8C with the evolution of aromatics from the degradation of
the styrene.[13] Figure 8, curve b, is the TG curve of the
GNSC8P/polystyrene composite. There are two steps in the
degradation of the composite: The first step, from 170 to
260 8C, is due to the existence of water in the GNSC8P lamellae
as well as the degradation of GNSC8P; the second step, roughly
from 400 to 450 8C, which is the degradation of the polymer,
has shifted to a higher temperature range than for pure
polystyrene. This indicates that there is a strong interaction
between the polymer matrix polystyrene and the GNSC8P at
the interface, and, because of this, the mobility of the polymer
segments near the interface has become suppressed. All the
above results indicate that introducing GNSC8P enhances the
formation of char on the surface of polystyrene and, as a
consequence, reduces the rate of decomposition.
3. Conclusions
We have successfully developed a simple, fast, and green
electrochemical method for the synthesis of GNSIL with just
one treatment step and with the assistance of an IL and water.
We are also gratified to obtain GNSIL/polystyrene nanocomposites with high structural homogeneity and excellent electrical
conductivity. Because our GNSILs can be easily prepared from
a vast array of graphite, their industrial production will become
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4.1 Preparation of GNSILs: All chemicals were used as received
without further purification. The ILs 1-octyl-3-methyl-imidazolium
hexafluorophosphate ([C8mim]þ[PF6]), 1-octyl-3-methyl-imidazolium
tetrafluoroborate ([C8mim]þ[BF4]), 1-octyl-3-methyl-imidazolium chlorine ([C8mim]þCl), and 1-butyl-3-methyl-imidazolium hexafluorophosphate ([C4mim]þ[PF6]) were donated by Changchun Institute of
Applied Chemistry, Chinese Academy of Science.
Two high-purity graphite rods (purchased from China National
Medicines Shenyang Co. Ltd.), placed parallel with a separation of
6.0 cm, were inserted as electrodes into the IL/water solution. A YJ26K
model potentiostat (Yongheng Precision Ammeter Co., China) was
used to provide the potential. Static potentials of 10–20 V were applied
to the two electrodes. After 30 min, the anode graphite rod was
corroded, and then a black precipitate gradually appeared at the
bottom of the reactor. Finally, the electrolyte formed a homogeneous
solution. The precipitate was taken out of the reactor after 6 h,
thoroughly washed with absolute ethanol, and dried in an oven for 2 h
at 60 8C. The product GNSIL was obtained.
4.2 Preparation of GNSIL/Polystyrene Composites: GNSIL/polystyrene
composites were prepared by a method similar to that of Stankovich
[11]. The dried GNSIL (100 mg) produced as described above was
stably and homogeneously dispersed in anhydrous DMF (100 mL) by
ultrasonic dispersion for 1 h (KQ-100DE ultrasonic bath, Kunshan
Ultrasonic Instrument Co., Kunshan, China, 75 W). Polystyrene
(molecular weight > 100000) was added to the above solution and
dissolved with stirring. Upon completion, the coagulation of the
polymer composites was accomplished by adding the mixed DMF
solutions dropwise into a large volume of vigorously stirred deionized
water (10:1 with respect to the volume of DMF used). The coagulated
composite powder was isolated via filtration, washed with deionized
water (200 mL), dried in an oven at 60 8C for 4 h, crushed into a fine
powder with a pestle and mortar, and then molded into a disc of 1.5 cm
diameter and typically 2 mm thick by pressing under 100 MPa at room
temperature. To convert weight percentage loading of GNSIL in the
composite samples to volume percentage (as used in the text), a density
for the GNSILs of 2.35 g cm3 was assumed along with the known
density of polystyrene, 1.03 g cm3.
4.3 Measurement and Characterization: TEM measurements were
conducted with a JEOL JEM-2010 microscope. The morphology was
also examined by a XL30 field-emission scanning electron microscope (FEI Company). AFM images were obtained in tapping mode
(SPA-400 SPM unit from Seiko, Japan). The TG patterns were
measured under N2 atmosphere with a Netzsch STA 409 8C thermal
analyzer at a heating rate of 10 8C min1. Electrical conductivity data
were obtained using a SDY-V four-probe instrument (Huayan
Instrument Co., China). X-ray powder diffraction (XRD) measurements of the as-prepared sample were performed on a Rigaku D/
max-IIB X-ray diffractometer with Cu Ka radiation (l ¼ 1.5418 Å).
FTIR spectra were obtained using a Nicolet MagNA-IR560 spectrometer. The Raman spectra of the products were recorded at ambient
temperature on a Spex 1403 Raman spectrometer with an argon-ion
laser at an excitation wavelength of 514.5 nm. UV-vis spectroscopy was
performed on a U-3010 spectrophotometer (Hitachi, Japan). The
graphite powder, scraped from the graphite rod, was ultrasonically
pretreated in DMF, and then the adsorption spectrum was measured.
ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Received: June 18, 2007
Revised: February 01, 2008
Published online: May 5, 2008
Adv. Funct. Mater. 2008, 18, 1518–1525
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